import java.util.Scanner;

/**
 * @Author YuanYuan
 * @Date 2022/4/29
 * @Time 15:01
 */
public class TestDemo {
    public static int fab(int n) {
        if(n == 1||n == 2){
            return 1;
        }else {
            return fab(n-1) + fab(n-2);
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        System.out.println(fab(n));
        //1 1 2 3 5 8 13 21
    }
}
